The light emitting diode (LED) emits lights in a single direction, the distribution range of light intensity is narrow, so the LED needs a lens to distribute the light. However the lights emitted from the LED is with small area and is not uniform enough after emitted from the present lens to be unable to satisfy the requirement of the application. Therefore many LEDs are used to be arranged to achieve that different points have the same and uniform light intensity in a same plane. It will lead to high cost and a heavy back light module system.